Track circuit apparatus



May 1l, 1937 H. G. WITMER ET AL 2,080,069

TRACK CIRCUIT APPARATUS Filed July 14, 1934 'H A 2,/ 43?' Ww H l 1' ih-6:1060 [il `5 L TR H=20w B fag-l. i B F4921@ 2; L 2l L' I 2 A@ l, A'. l) A I.

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U s/H "1T BXCX l 2x j R4 4', -J- F- u l 1 X A fx A .8. B Fl. Y mda g; By Claude M Hz'nves THEIR ATTORNEY n Patented May 11, 1937 UNITED STATES PATENT OFFICE TRACK CIRCUIT APPARATUS Application `luly 14, 193,4, Serial No. 735,210

13 Claims.

Our invention relates to track circuit apparatus and more specifically to apparatus for increasing the shunting sensitivity of track circuits.

We will describe several forms of track circuit apparatus embodying our invention, and will then point out the novel features thereof in claims.

Fig. 1 of the accompanying drawing is a` diagrammatic view showing one form of apparatus embodying our invention. Figs. la, 1b, and 1c are diagrammatic views showing equivalent cir cuits which are used for explaining the operation of certain portions of the apparatus of Fig. l. Figs. 2, 3, 4, 5, and 6 are diagrammatic views showing modified forms of the apparatus of Fig. 1, also embodying our invention. Figs. '7 and 8 are diagrammatic views embodying our invention and showing modified forms of the apparatus of Fig. l, in which the track relay does not occupy its`customary position at the end of the track circuit.

Similar reference characters refer to similar parts in each of the severalviews.

Referring to Fig. l, the reference characters I and 2 designate the rails of a section of railway track. Connected across the rails at one end of the section is a source of current B which supplies curr-ent through a limiting resistor R, to a track relay TR which is connected across the rails at the other'end of the section. In contact with the track ballast is a conductor A, which is electrically connected with that terminal of resistor R which makes connection with the source B. Conductor A is preferably a scrap rail of suitable length spiked to the same ties which support the rails i and 2, in a manner to simulate as closely as possible the type of junction which exists between the rails l and 2 and the supporting ties and ballast. That is, the connection of conductor A with the ballast should be such that a given length of this conductor will have a resistance to ground of approximately the same value as exists between a corresponding length of either rail or rail 2, to ground. It is not essential that conductor A be in the form of a rail, as any suitable bared conductor, such, for example, as a copper or iron wire making contact with the ballast through the ties, or in any other suitable manner, can be used. For example, an insulated wire bared at those portions which are spiked or otherwise fastened to the ties, can also be used.

Experience with track circuit operation appears to indicate that the major portion of the track ballast resistance is probably concentrated in a comparatively thin film which forms the junction between a rail and its supporting ties, as well as, to some extent, in a second film at the area of contact of a tie with the ballast in which it is imbedded. Based on these observations, the particular location of conductor A with respect to rails l and 2 is relatively unimportant, provided that substantial contact with the rail supporting ties is obtained for the purpose of establishing a film resistance condition at the conductor-tie junction which will closely approximate the film resistance condition at the rail-tie junction, under different conditions of ballast resistance. Ballast conductor A can be placed on the outside of rail l or rail 2, if desired, or it can take the form of a guardrail. If the lballast conductor is placed near to rail 2, trunking or other covering or insulation should be used in order to avoid accidental short-circuits with rail 2 which might result in over-energization of the track relay.

In explaining the operation of the track circuit system of Fig. 1, we shall make use of Figs. 1a, 1b, and 1c. Referring to Fig. la., let it be assumed that with a track circuit of given length, under the condition of minimum ballast resistance, the combination of the four resistances R, R1, R2, and R6, when R has a resistance of 20 ohms, and R1, R2 and Reach have a resistance of l0 ohms, is proper for causing battery B to supply just enough current to pick up relay TR. Conductor A is chosen of sunicient length to provide a resistance R6 of 10 ohms from this conductor to ground, and to simplify the explanation it will be assumed that rails l` and 2 each have a resistance of l0 ohms to ground, so that'R1 and R2 are each 10 ohms. From the diagramin Fig. 1a, it will be apparent that resistance R is in multiple with the two series resistances R6 and R2, so that these three resistances are equivalent to the single ohm resistance Re of Fig. lbf. If the drop across R.6 due tothe current flowing in R1 is neglected, then the electrical conditions may be represented by the diagram of Fig. 1b, which indicates that under wet ballast conditions the track circuit operates with the same effect as though relay TR were supplied with current through a 10 ohm limiting4 resistor at the battery. For the purpose of showing that applicants apparatus improves shunting sensitivity by permitting a limiting resistor R of higher value to be used, Fig. lb is sufciently accurate. It should be understood, however, that the above mentioned drop which occurs across resistor R6 would in practice require a readjustment in the values of resistors R6, R1, and R2 in the example given in order that the proper relay operating current might be obtained.

The conditions existing when the ballast dries out are indicated in Fig. lc. Resistors R1, R2, and

R6 are now infinite, and the limiting resistor R has an effective value which is the same as its actual value, namely, 20 ohms. That is, the shunting sensitivity under the dry ball-ast condition is that which corresponds to a 20 ohm battery resistor. If the conductor A were not used, the value of resistor R would have to be 10 ohms, in the example illustrated, in order that relay IR would receive suicient pickup current under the wet ballast condition. Consequently, after the ballast became dry, the shunting sensitivity would be that corresponding to 10 ohm battery resistor. Since the shunting sensitivity is largely determined by the -amount of resistance in series with the track battery, and the amount of current flowing through the track relay, the marked advantage of the apparatus and method disclosed becomes obvious from the consideration that a high resistance causes a relatively large potential drop when the track circuit becomes occupied, thus robbing the track relay of energy, and this high resistance also causes a relatively small current to flow through the track relay, so that with the track occupied, a smaller change in track relay current is required to cause the track relay to release.

From the above explanation, it is clear that a train shunt of much higher resistance will be effective in causing relay TR to release if conductor A is used, than if the usual type of track circuit is employed. It will be understood that the resistance value of R6 need not be equal to the value of R2 or R1 nor need R6 plus R2 be equal in value to the fixed resistor R, these values being merely explanatory and being determined, in actual practice, by the physical characteristics of the` particular track circuit, character of rail traflic, degree of shunting sensitivity required, as Well as other practical considerations. If it is desired to limit the amount of battery current which flows through the shunt path formed by resistances R1 and R6, or to limit the current flow upon the occurrence of an accidental short circuit between conductor A and rail I or rail 2, a physical resistor R3 can be inserted in the connecting wire 3, as indicated in Fig. 2. Also, a fuse may be used in place of resistor R3, or in addition thereto.

Referring now to Fig. 3, we have shown how the principle of Fig. 1 may be applied to an alternating current track circuit to improve the shunting sensitivity. 'I'he relay TR is an alternating current track rel-ay of either the single-element 01 double-element type, which is supplied with rail current from a track transformer T, which, in turn, is energized from a suitable source of alternating current having the terminals BX-CX. The rail current from transformer T is supplied through a series resistor R, around which is connected the ballast conductor A, in the same manner as in Fig. 1. The manner in which the apparatus of Fig. 3 operates will be clear without detailed explanation, from the fact that the effective resistance of resistor R will be low under wet ballast conditions, and will be high under dry ballast conditions, thus aiding to lower the relay current, or render the phase angle less favorable, or both, ata time when the usual type of track circuit provides the lowest shunting sensitivity.

In Fig. 4, we have shown how the ballast conductor A may be applied to a reactor-fed track circuit, the principle of operation being the same as in Fig. 3.

In Fig. 5, ballast conductors are applied at both ends of the track circuit. At the feed end, rail current is supplied from a source of current having the terminals C-D, through a limiting impedance J of any suitable character. At the receiving end, is a load, or receiving device L which receives current through another impedance K. The ballast conductors A and A1 operate on the impedances J and K, respectively, in such a manner as to prevent a wide variation in the current taken by the load L, when the ballast resistance varies between wide limits.

Fig. 6 shows how the resistor R of Figs. 1 or 3 may be divided into two parts R4 and R5, for the purpose of limiting the amount of current taken from battery B in the event 0f a short-circuit between conductor A and rails l or 2.

In the arrangement illustrated in Fig. '7, both the track relay TR and track current source T are at the same end of the track circuit. Relay TR is an ordinary direct current relay, and is operated in part from the potential drop across the limiting resistor R. This potential drop, although supplied from the alternating current source BX-CX, has a prominent unidirectional component due to the rectier load F which is connected across the rails at the other end of the track circuit. Because of the connection of ballast conductor A between resistor R and the track transformer secondary, relay TR also receives energy from the potential drop across the ballast path which is in parallel with resistor R, and which includes conductor A.

Resistor R should be of such a value that under innite ballast conditions, relay TR will receive normal energy. Consequently, as the ballast resistance decreases, the equivalent resistance of resistor R and the ballast conductor path in parallel therewith will decrease also, andthe current dr-awn from transformer T will therefore increase. As a result, the drop across the equivalent resistance will remain substantially the same whether the ballast is Wet or dry, so that the track relay energization will also remain approximately at its normal value, and shunting sensitivity will accordingly be increased.

In Fig. 8, relay TR is connected directly across the track rails, rather than across resistor R, as in Fig. '7. The operation of the circuit of Fig. 8 is otherwise the same as that of Fig. '7, namely, a change in ballast resistance changes the amount of current owing over the path which includes the ballast conductor A, whereby the drop across resistor R and the voltage impressed across the rails remain subtantial'ly constant.

In conclusion, it will be noted that the track circuits herein disclosed provide a shunting sensitivity under dry ballast conditions which is much greater than that provided by the ordinary track circuit. The shunting sensitivity under conditions of wet ballast can be at least as high as that which is normally obtained. By properly proportioning the resistance values of R and R2 of Fig. la, the energization of relay 'IR can actually be made to decrease under dry weather conditions, so that the shunting sensitivity will be lowest under the condition of wet ballast. This situation is the reverse of that obtaining with ordinary track circuits, which are usually more difficult to shunt when the ballast is dry. In the usual type of track circuit, for reasons which will be clear to those versed in the art of track-circuiting, the optimum value of train shunt resistance which can be depended on for shunting is that which is equivalent to the total minimum ballast resistance of the track circuit. In the track circuitwhich we have provided, however, due to the fact that a part of ythe current for operatingy the track relay is the ballast resistance in multiple with lthe remaining part -which is supplied throughA the physical resistor R, shunt resistance which can bei depended on vfor shunting can beI madesubstantially higherthan the -aforementionedtotal rninimumballast resistance'ofthe track circuit. Y

Although we have herein shown anddescribed only a few forms ofA apparatus embodying 'our invention, it is understood that various-changes andV modiiications maybe made therein within the scope ofy the`=apperrdedclaims without departing from the spirit and scope of our invention.

Having thus described our invention, what we claim is:

1. In combination, a section of railway track, a source of track circuit current connected across the two rails of said track, a current limiting device connected between said source and one rail of said track, and a conductor in contact with the track ballast and joined electrically with said device at the connection between said device and said source for varying the eiectiveness of said device when the resistance of said track ballast changes.

2. In combination, a sectionof railway track, a source of current connected across the rails at one end of said section, a track relay connected across the rails at the other end of said section, an impedance connected between sai-d source and one rail of said track, and a conductor in contact with the track ballast and joined electrically with said impedance at the connection between said impedance and said source for preventing a substantial increase in the current supplied to said track relay when the resistance of said track ballast increases.

3. In combination, a section of railway track, a source of track circuit current connected across the rails of said track, a current limiting device connected between said source and one rail of said track, and a conductor joined electrically with said device at the connection between said device and said source, said conductor being placed in contact with the track'ballast in such manner as to substantially duplicate the connection of the running rails of said track with the ballast, for varying the effectiveness of said device when the resistance of said track ballast changes.

4. In combination, a section of railway track, a source of direct current for said section, a direct current track relay receiving current from the rails of said section, a resistor connected between said source and one rail of said track, and a ballast conductor in contact with the track ballast and joined electrically with said resistor at the connection of said resistor with said source for varying the eiective value of said resistor with changes in the ballast resistance whereby the current received by said track relay will be maintained substantially constant.

5. In combination, a section of railway track, a source of alternating current for said section, an alternating current track relay receiving current from the rails of said section, an impedance connected between said source and one rail of said track, and a ballast conductor in contact with the track ballast and joined electrically with said impedance at the connection between said impedance and said source for preventing a substantial increase in the current supplied to said track resupplied through the optimum value of train lay-when the' resistance of said=track` ballast increases. i

6r In combination, a section of railway track;

a track circuit for said section including the two rails of said track, al source of `current connected across said-railsA atione end of they section, and ar track relay connected across said-two rails at tl1 `e`oi",h'er endof the section; an impedance conneetedbetween said source and one rail of -said track, `and a conductorjoined electrically with said impedance' at thev connection between said impedance andisaidlsource and making contact with-.the trackballast-in such manner as to substantially duplicate-the connection of said rails withl the"ballast,-forE improv-ing: the shunting sensitivity of said track circuit when the resistance of said ballast increases.

I1. A track circuit the ballast leakage resistance of which is subject to variation with weather conditions, a source of current and a track relay for said track circuit, and means for normally supplying current from said source to said track relay over two paths, one of which includes a current-limiting impedance, and the other of which includes a ballast conductor in contact with the track ballast, whereby if said ballast becomes dry, the resistance of said other path will increase to limit the current supplied to said track relay.

8. A track circuit ance of which is subject to variation with weather conditions, a source of current and a track relay for said track circuit, and means for normally supplying current from said source to said track relay over two paths, one of which includes a current-limiting impedance, and the other of which includes a ballast conductor making contact with the track ballast in such manner as to substantially duplicate the ballast connection of the running rails which form a part of said track circuit, whereby if the ballast resistance increases, the resistance of said other path will also increase t`o limit the current supplied to said track relay.

9. In combination, a section of railway track, a source of current connected across the rails at one end of said section, a load connected across the rails at the other end of said section, an impedance connected between said source and one rail of said track, and a ballast conductor in contact with the track ballast and joined electrically with said impedance at the connection between said impedance and said source for limiting the current supplied to said load when the resistance of said ballast increases.

10. In combination, a section of railway track, a source of current, a track relay, and means for supplying current from said source to said track relay, said means comprising two paths, one of which includes a xed impedance and the rails of said section, and the other of which excludes said xed impedance and includes a portion of the track ballast and said rails, whereby the current supplied to said track relay will be limited when the resistance of said track ballast increases.

11. In combination, a section of railway track, a source of current connected across the rails at one end of said section, a load connected across the rails at the other end of said section, a first impedance connected between said source and a rail of said track, a first ballast conductor in contact with the track ballast and joined electrically with said rst impedance at the connection thereof with said source, a second impedance conthe ballast leakage resistnected between said load and a rail of said track, when the resistance of said track ballast changes. and a second ballast conductor in contact with 13. In combination, a section of railway track, the track ballast and joined electrically with said a source of track circuit current connected across second impedance at the connection thereof with the rails at one end of said section, a track relay 5 said load. connected across the rails at the other end of 12. In combination, a section of railway track, said section, a first and a second impedance cona source of track circuit current connected across nected in series between said source and one rail the two rails of said track, a first impedance conof said track, and a ballast conductor in contact nected between said source and one rail of said with the track ballast and joined electrically with 10 track, a second impedance, and a ballast consaid two impedances at the connection therebeductor in contact with the track ballast and tween, for limiting the current supplied to said ljoined electrically with said rst impedance track relay when the resistance of said ballast through said second impedance at the connecincreases.

tion of said first impedance with said source, for HAROLD G. WITMER. 15 Varying the eective Value of said rst impedance CLAUDE M. HINES. 

